The present invention relates to a rod-and-groove arrangement for sealing and/or adjusting the axial location at adjoining parts of a turbine.
Turbines, e.g., steam turbines, typically comprise inner and outer shells accurately axially positioned relative to one another. The inner shell also carries fixed stator blades, e.g., partitions, which likewise must be accurately axially located relative to the inner shell. Substantial difficulty is encountered in adjusting the axial locations of these various turbine parts during installation. This difficulty is exacerbated during routine maintenance or during other outages in the field when the turbine is disassembled for repair. Moreover, certain of these parts at axially optimized locations must also be sealed to one another.
Currently, axial positioning between inner and outer turbine shells is accomplished by disposing the lower inner shell half in the lower outer shell half, optimizing the axial position of the shells, locating the rotor in the lower inner shell half and shifting the lower inner shell half axially to an optimum axial position relative to the rotor, e.g., within two or three mils. It is then necessary to secure or lock the lower inner and outer shells to one another in the optimum relative axial position. To maintain these parts of the turbine in their optimum axial positions relative to one another and also to seal the parts to one another, seal/positioning strips have been used previously which are either square or rectangular in cross-sectional shape. The strips are sized to fit into mating grooves and are typically rolled or peened into place. These strips must be inserted and seated in the bottom of the groove to ensure that the optimum axial position can be duplicated during final assembly from an original measured position. Thus, the components of the turbine whose axial positions have been measured and determined to be optimum are removed from the assembly along with the strips whose later reinstallation ensures that the parts are maintained in the optimum axial position in final assembly. That is, the lower inner shell half is disposed in the lower outer shell half, the diaphragms are loaded into the lower inner shell half, and the rotor is inserted into the lower inner shell half. After the axial positions are optimized and the seal/positioning strips are fabricated for maintaining clearances between the lower inner and outer shell halves, as well as between the diaphragms and the inner shell, the rotor and lower inner shell half are removed from the lower outer shell half. The clearance strip(s) are peened or rolled into locked positions in the lower inner shell half and diaphragms and these components are reassembled. The upper inner and outer shells are then assembled onto the turbine.
Further, the prior square or rectangular seal/positioning strips can be a source of high-stress areas, particularly if the groove corner radii are not designed properly. The strip must also be inserted and seated in the bottom of the groove identically as previously disposed to ensure the axial position duplicates the original measured position. The same is true with respect to locating diaphragms and the partitions carried thereby relative to the inner shell. Consequently, there has developed a need for an apparatus and a method for maintaining the desired optimum axial positions of components of a turbine without removal of the components from locations in the desired axial positions relative to one another and also to seal the parts to one another.
In accordance with a preferred embodiment of the present invention, one of the axially facing surfaces on a turbine part, for example, an inner shell, is provided with a groove having a generally cylindrically shaped cross-section opening through the one surface and having a centerline along the groove offset toward the one surface. For example, an axial positioning surface of the lower inner shell half of a steam turbine is provided with a groove extending 180xc2x0 and which groove is generally cylindrical in cross-section and opens through the axial facing surface. An arcuate rod having a generally cylindrical cross-section is fabricated for disposition in the groove with a tight tolerance therebetween. For example, the rod has a generally cylindrical cross-section corresponding to the cylindrical cross-section of the groove. The rod also has a flat surface coextensive with its length and which is formed to a measured distance from the axis of the rod prior to installation. When the rod is received within the groove, the flat surface projects a predetermined distance from the part surface. By forming both the groove and rod in cylindrical cross-sections, insertion of the rod lengthwise into the groove automatically captures the rod in the groove preventing axial movement out of the groove. The closely toleranced match of cylindrical surfaces eliminates the need to peen or weld the rod to the part while retaining optimized accurate axial locations of the turbine parts.
The rod is preferably formed in arcuate segments, for example, on the order of 15-20xc2x0. In this manner, the flat surfaces along the rod segments can be formed in the field or at the site of the original equipment manufacture by readily available conventional grinding machines. The rod segments are also pre-bent to generally correspond to the radius of the groove. Thus, with the turbine parts assembled in optimized accurate axial positions, the rod segments are ground to form the flat surfaces at a precise measured distance to maintain the precise axial spacing between the parts. The rod segments are then inserted into the groove in a circumferential direction. The cylindrical surfaces of the rod segments engage the mating cylindrical surfaces of the groove and the flat surface of the rod segments engage the opposing surface of the other turbine part. Neither turbine part requires removal in order for the rod segments to be installed. Consequently, the previously required steps of removing the rotor from the lower inner shell half and the lower inner shell half from the lower outer shell half in order to peen or roll in the seal/positioning strips are entirely eliminated.
Further, the rod segments also perform a sealing function. For example, where the rod segments are employed between the diaphragms and axially opposed surfaces of the inner shell, the flat surfaces form seals with the opposing surface. The adjoining ends of the rod segments also butt one another to form seals. To ensure sealing capacity, the ends may have slots for receiving the splines or may have a tongue-and-groove arrangement whereby a supplemental seal is formed between the butting end faces of the rod segments.
Various advantages accrue to the use of the rod segments and grooves. For example, the rod segments are captured within the groove without the necessity of peening or welding the strips in place. The flat surfaces on the rod segments can be formed using conventional tooling, i.e., a surface grinder. By using mating cylindrical surfaces of the rod segments and a groove, stresses in the component part carrying the groove are minimized or eliminated. Further, because the rod segments are pre-bent to have a radius, each segment will fit tightly in the groove, creating a friction-locking effect due to the arch of the rod segments. Importantly, the segments can be inserted without removing the assembled turbine components.
In a preferred embodiment according to the present invention, there is provided apparatus for locating or sealing surfaces of a turbine comprising first and second turbine parts having opposed flat surfaces and an elongated groove in one of the surfaces, the elongated groove having generally cylindrically shaped side walls and a groove centerline offset toward the one surface, the groove opening through the one surface, a rod disposed in the groove, the rod being generally cylindrical in cross-section and having an axis coincident with the centerline of the groove, the rod having a flat surface coextensive therewith and generally parallel to the axis, the flat surface projecting from the groove beyond the one surface thereof and lying generally parallel thereto for engagement with the opposing surface enabling the rod to locate or seal the respective surfaces relative to one another.
In a further preferred embodiment according to the present invention, there is provided a method of axially locating first and second parts of a turbine comprising the steps of (a) forming a groove in an axially facing flat surface of one of the first and second turbine parts, with the groove opening through the surface and having a centerline offset toward the surface, (b) forming a rod having a cross-section generally corresponding to the cross-section of the groove and a flat surface along a side of the rod coextensive with the rod and (c) disposing the rod in the groove with the flat surface of the rod spaced axially outwardly of the groove and the surface of the one part for engaging the second part to space the first and second turbine parts in adjusted axial position relative to one another.
In a further preferred embodiment according to the present invention, there is provided a method of sealing or locating first and second parts of a turbine to one another, comprising the steps of (a) forming a groove in an axially facing surface of one of the first and second turbine parts with the groove opening through the surface and having a centerline offset toward the surface, (b) forming a plurality of rod segments each having a cross-section generally corresponding to the cross-section of the groove and having a flat sealing surface along a side of the rod segment and coextensive therewith and (c) disposing the rod segments in the groove one after another with the flat surface of the rod spaced axially outwardly of the groove and the surface of the one part for sealing or locating the second part of the turbine relative to the one part.